1. Field of the Invention
The present invention relates to an electric car controller and more particularly to the apparatus and method for detecting an error of current detecting means for detecting the current of an alternating current motor.
2. Description of Prior Art
A controller for detecting an error of current detecting means in an alternating current motor driving apparatus is disclosed in JP A 09-172791 and JP A 2000-116176, for example.
The JP A 09-172791 discloses a technique, wherein an alternating current motor is controlled according to the voltage command value of the voltage to be applied to the motor or current command value representing instantaneous current by making reference to the current value of the motor detected by a current sensor, and comparison is made between the current value of the motor detected by the current sensor and the motor current value estimated from the voltage command or current command value, whereby evaluation is made to determine that an error has occurred to the current sensor or related circuit and electric power system.
The JP A 2000-116176 describes a technique of using;
a first estimating means for estimating the current of the remaining one phase based on the current detected value by controlling a three-phase alternating current motor and detecting 2-phase current through a current sensor for two phases, and
a second estimating means for estimating the current for one phase from the current phase angle and current detected value for remaining two phases, whereby the first estimated current value and second estimated current value each are obtained, and they are compared with each other to evaluate an error of the current sensor.
In the aforementioned prior arts, the JP A 09-172791, for example, discloses the configuration of making a direction comparison between the detected value of an current sensor as alternating current and the voltage command value to be applied to a motor or instantaneous current command value. However, the controller also places under feedback control the current value detected by a current sensor, thereby ensuring that the current itself flowing to the motor will follow the command. In this configuration, control is made by making comparison between the current detected value and voltage command value or instantaneous current command value. If an error has occurred to the current sensor or electric power system, the controller provides feedback control to ensure that the current flowing to the motor will follow the voltage command value or instantaneous current command. As a result, when the output gain of the current sensor has reduced, for example, the feedback control of the controller is made to ensure that the voltage command value or current command value will be followed for the phase subjected to reduction in the output gain of the current sensor. As a result, excessive current may flow to that phase, or a balance between the current detected value and command value may be maintained ultimately. A sufficient consideration is not given especially to evaluation of a current sensor error, according to this prior art.
Similarly in the JP A 2000-116176, feedback control is made by making comparison and reference to the current command value and current detected value. The estimated current value used for error evaluation is based on the current value detected by the current sensor. Accordingly, when an error has occurred to the current sensor, there may be a case where a balance is kept between current command and current detected value. A current sensor error may not be evaluated.
An object of the present invention is to provide a electric car controller and control method capable of evaluating an error in a manner appropriate to each of various aspects of errors occurring to current detecting means.
Another object of the present invention is to provide an electric car controller and control method which allow continuous operation even if an error has occurred to current detecting means for one of three phases.
Still another object of the present invention is to eliminate the use of unnecessary current detecting means by allowing separate evaluation of each error of current detecting means, thereby ensuring reduction in the apparatus cost.
An electric car controller designed to attain the above object provides dq-axis vector current control for separate and independent control of primary current to be supplied to a stator of an alternating current motor based on a q-axis control current command value and a d-axis control current command value, and provides current feedback control by detecting the primary current of the aforementioned alternating current motor by current detecting means.
The aforementioned controller comprises;
an operation processing unit for generating a control current command value based on a command value to supply it to the aforementioned alternating current motor and for performing current feedback control through detection by the aforementioned current detecting means and conversion by current converting means, and
an evaluation processing unit for generating a current command value for evaluation and performing evaluation to see if the aforementioned current detecting means is normal or not. The aforementioned evaluation processing unit is characterized by comprising;
a step of generating an evaluation current command value for comparison and evaluation unaffected by the aforementioned current feedback and independently of the aforementioned control current command value, based on the aforementioned q-axis control current command value and the aforementioned d-axis control current command value using command value converting means,
a step of comparing between an alternating current detected value detected by the aforementioned current detecting means without being converted by the aforementioned current converting means and the aforementioned evaluation current command value, and
a step of determining that the aforementioned current detecting means is incorrect if the result of comparison has exceeded a threshold value.
In the present invention, it is preferred that the current indication value for the aforementioned evaluation be calculated for any desired combination of two phases out of three, and the aforementioned alternating current detected value be a detected value for any desired two phases out of three. The aforementioned two-phase evaluation current indication value and alternating current detected value are compared with each other separately for each phase. If an error is found in either one or both of two phases, then the operation of the aforementioned electric car controller is suspended.
In the present invention, it is preferred that the aforementioned evaluation current indication value be calculated for three phases, and the aforementioned alternating current detected value be a detected value for three phases. The aforementioned three-phase evaluation current indication value and alternating current detected value are compared with each other separately for each phase. If an error is found in any one or both of three phases, then the estimated detection value of the aforementioned alternating current for the affected phase is calculated and generated based on the aforementioned alternating current detected value for the remaining two phases whereby the operation of the aforementioned electric car controller is restricted or continued.
In the present invention, it is preferred that the operation of the aforementioned electric car controller be suspended if an error is found in two of three phases or in all the three phases.
The present invention is further characterized by an electric car control method comprising;
a step of regulating the amplitude and phase of the primary current to be supplied to an alternating current motor and controlling the speed or torque of said alternating current motor, by dq-axis vector current control which provides separate and independent control of the primary current supplied to the stator of said alternating current motor, namely, a q-axis current component as a torque component based on a q-axis control current command value and a d-axis current component as an exciting component based on a d-axis control current command value,
a step of applying said primary current to said alternating current motor and controlling it through electric power converting means, and
a step of detecting said primary current to said alternating current motor an alternating current detected value through current detecting means:
said electric car control method comprising;
a step of providing feedback current control by detecting said primary current as a q-axis current detected value and a d-axis current detected value and converting it through current converting means, and by comparing between said q-axis control current command value and said q-axis current detected value, and between said d-axis control current command value and said d-axis current detected value,
a step of generating an evaluation current command value for comparison and evaluation independently of said feedback control current command value based on said q-axis control current command value and said d-axis control current command value,
a step of comparing said alternating current detected value as an alternating current component detected by said current detecting means without being converted, and said evaluation current command value, and
a step of determining that said current detecting means is incorrect if the result of comparison exceeds a threshold value.
According to the present invention, an evaluation current command value independently of the current command value for feedback control is generated. This is compared with the alternating current detected value as an alternating current component detected by current detecting means without being converted, and evaluation is made. Thus, the present invention provides an electric car controller and control method capable of adequate evaluation of an error in response to each of various troubles occurring to current detecting means.